Patent Document 1 discloses a controller equipped with inverters of plural systems that switchingly energize plural coil sets of a motor. In the controller, the total sum of phase currents is calculated at each system. If a difference in the total phase current between two systems deviates from a predetermined range, it is determined that the two systems are short-circuited. When the short-circuit is detected as above, either one of the two systems, which are compared to obtain the difference in the total phase current, is stopped.